Liquid Crystal Display Module

ABSTRACT

A liquid crystal display module includes a liquid crystal display panel, a backlight device arranged on a back surface of the liquid crystal display panel, the backlight device being constituted of a light guide plate and a reflection sheet arranged on a back surface of the light guide plate, an insulation sheet arranged on a back surface of the light guide plate, a flexible printed circuit board having one end thereof mounted on the liquid crystal display panel and another end thereof formed on a back surface of the insulating sheet, and at least one LED formed on the flexible print board and faced to the light guide plate. The reflection sheet, the insulation sheet, and the flexible print board extend over different distances from the at least one LED in this order.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/971,936, filed Jan. 10, 2008, the contents of which are incorporatedherein by reference.

The disclosure of Japanese Patent Application No. 2007-3979 filed onJan. 12, 2007 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a liquid crystal display module, andmore particularly to a miniaturized liquid crystal display module suchas a mobile phone.

2. Description of Related Art

Currently, a small-sized liquid crystal display panel having a size ofapproximately 2 inches to 4 inches has been used as a mobile phone. Themobile phone includes a liquid crystal display module which isconstituted of a liquid crystal display panel and a backlight devicearranged on a back surface of the liquid crystal display panel, and acasing for storing the liquid crystal display module.

Here, although there is no direct relationship with the invention,patent document 1 (JP-A-11 (1999)-305228) discloses a technique forfixing a reflection sheet using a double-sided adhesive tape.

SUMMARY

FIG. 5 is a perspective view showing the constitution of a conventionalliquid crystal display module.

A liquid crystal display panel is constituted by overlapping a TFTsubstrate 11 and a color filter substrate 12 (hereinafter, referred toas a CF substrate) with a liquid crystal layer sandwiched therebetween.Further, on a portion of the TFT substrate 11 where the TFT substrate 11and the CF substrate 12 do not overlap each other, a driver chip 13 forcontrolling driving of the liquid crystal display panel is formed.Further, for supplying signals to the driver chip 13, one end of aflexible printed circuit board 15 is arranged on the portion of the TFTsubstrate 11 where the TFT substrate 11 and the CF substrate 12 do notoverlap each other. Further, a polarizer 14 is arranged on the CFsubstrate 12, and a polarizer is also arranged on the TFT substrate 11.

The liquid crystal display panel is arranged on an upper side of aframe-shaped mold frame 16. Further, on a lower side of the mold frame16, optical sheets such as an upper diffusion sheet, an upper prismsheet, a lower prism sheet and a lower diffusion sheet not shown in thedrawing, a light guide plate 17, and a reflection sheet 19 are arrangedin a state that these optical sheets, the light guide plate 17 and thereflection sheet 19 are sandwiched between a portion of the other end ofthe flexible printed circuit board 15 described above and the mold frame16. Here, on the other end of the flexible printed circuit board 15, alight source 18 such as an LED is arranged to face a side surface of thelight guide plate 17 in an opposed manner.

FIG. 6 is a view showing a cross-sectional constitution of theconventional liquid crystal display module taken along a line A-A′ inFIG. 5. FIG. 6 shows a state that the liquid crystal display moduleshown in FIG. 5 is stored in a space defined by an upper frame 21 and alower frame 22. Further, FIG. 7 is a view showing a cross-sectionalconstitution of the conventional liquid crystal display module takenalong a line B-B′ in FIG. 5. FIG. 7 shows a state that the liquidcrystal display module shown in FIG. 5 is stored in the space defined bythe upper frame 21 and the lower frame 22 in the same manner as FIG. 6.

As shown in FIG. 6, the other end of the flexible printed circuit board15 is arranged to overlap a portion of the reflection sheet 19. Further,as shown in FIG. 7, to the other end of the flexible printed circuitboard 15, a pushing force is applied from below by the lower frame 22made of metal, for example. It has been found that, due to such apushing pressure, the other end of the flexible printed circuit board 15is brought into contact with the reflection sheet 19, and as a result,the reflection sheet 19 is deflected thus generating displayirregularities.

The invention has been made to overcome such drawbacks, and it is anobject of the invention to provide a liquid crystal display module whichcan prevent the generation of display irregularities even when theliquid crystal display module having a relatively large display screenis stored in a casing having a relatively small storing space.

According to one aspect of the invention, there is provided a liquidcrystal display module which includes a liquid crystal display panel anda backlight device arranged on a back surface of the liquid crystaldisplay panel, wherein the backlight device is constituted of a lightguide plate and a reflection sheet which is arranged on a back surfaceof the light guide plate, the liquid crystal display module includes aflexible printed circuit board having one end thereof mounted on theliquid crystal display panel and the other end thereof formed on a backside of the reflection sheet in an overlapping manner, and an insulationsheet arranged between the other end of the flexible printed circuitboard and the reflection sheet.

Due to such a constitution, it is possible to provide a liquid crystaldisplay module which can prevent the generation of displayirregularities.

Further, in the liquid crystal display module, the insulation sheet hasa thickness thereof set to a value not less than 20 μm and not more than50 μm. Here, with respect to the thickness of the insulation sheet, whenthe thickness is set to a value not less than 30 μm and not more than 50μm, it is possible to further expect the above-mentioned advantageouseffect of the invention. The thickness of the insulation sheet ispreferably set to a value not less than 35 μm and not more than 45 μm.

Further, in the liquid crystal display module, the other end of theflexible printed circuit board overlaps a portion of the reflectionsheet, and the insulation sheet is arranged on the reflection sheet in astate that the insulation sheet gets over the other end of the flexibleprinted circuit board.

Further, in the liquid crystal display module, the insulation sheet isarranged on the reflection sheet in a state that the insulation sheetgets over the other end of the flexible printed circuit board by atleast 10 mm or more.

It is considerable that the insulation sheet of the invention ispreferably made of a material having a smooth surface such aspolyethylene terephthalate sheet (PET sheet), for example.

Here, in the above-mentioned liquid crystal display module, the lightsource is arranged on the other end of the flexible printed circuitboard, and the light source faces one side surface of the light guideplate in an opposed manner. Further, in the liquid crystal displaymodule, optical sheets such as an upper diffusion sheet, an upper prismsheet, a lower prism sheet and a lower diffusion sheet are arrangedbetween the light guide plate and the liquid crystal display panel.

According to the invention, it is possible to provide a liquid crystaldisplay module which can prevent the generation of displayirregularities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the constitution of a liquid crystal displaymodule 10 according to the invention;

FIG. 2 is a view showing the cross-sectional constitution of the liquidcrystal display module of the invention taken along a line A-A′ in FIG.1, and showing a state that the liquid crystal display module is storedin a space defined by an upper frame 21 and a lower frame 22;

FIG. 3 is a view showing the conventional cross-sectional constitutionof the liquid crystal display module taken along a line B-B′ in FIG. 1,and showing a state that the liquid crystal display module is stored ina space defined by an upper frame 21 and a lower frame 22;

FIG. 4 is a view showing the constitution of an insulation sheet of theinvention;

FIG. 5 is a perspective view showing the constitution of a conventionalliquid crystal display module;

FIG. 6 is a view showing the cross-sectional constitution of theconventional liquid crystal display module taken along a line A-A′ inFIG. 5, and showing a state that the conventional liquid crystal displaymodule is stored in a space defined by an upper frame 21 and a lowerframe 22; and

FIG. 7 is a view showing the cross-sectional constitution of theconventional liquid crystal display module taken along a line B-B′ inFIG. 5, and showing a state that the conventional liquid crystal displaymodule is stored in the space defined by the upper frame 21 and thelower frame 22.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the constitution of a liquid crystal display module 10according to the invention.

A liquid crystal display panel is constituted by overlapping a TFTsubstrate 11 and a color filter substrate 12 (hereinafter, referred toas a CF substrate 12) formed of an insulative transparent substrate suchas a glass substrate, a plastic substrate or the like, for example, witha liquid crystal layer sandwiched therebetween. Further, on a portion ofthe TFT substrate 11 where the TFT substrate 11 and the CF substrate 12do not overlap each other, a driver chip 13 for controlling driving ofthe liquid crystal display panel is formed. Further, for supplyingsignals to the driver chip 13, one end of a flexible printed circuitboard 15 is arranged on the portion of the TFT substrate 11 where theTFT substrate 11 and the CF substrate 12 do not overlap each other.Further, a polarizer 14 is arranged on the CF substrate 12, and apolarizer is also arranged on the TFT substrate 11. Here, for arrangingthe driver chip 13 on the TFT substrate 11, the CF substrate 12 is madesmaller than the TFT substrate 11. It is needless to say that when thedriver chip is arranged on the CF substrate 12, the CF substrate 12 ismade larger than the TFT substrate 11 in size.

The liquid crystal display panel is arranged on an upper side of aframe-shaped mold frame 16. Further, on a lower side of the mold frame16, optical sheets such as an upper diffusion sheet, an upper prismsheet, a lower prism sheet and a lower diffusion sheet not shown in thedrawing, a light guide plate 17, and a reflection sheet 19 are arrangedin a state that these optical sheets, the light guide plate 17 and thereflection sheet 19 are sandwiched between a portion of the other end ofthe flexible printed circuit board 15 described above and the mold frame16. Here, on the other end of the flexible printed circuit board 15, alight source 18 such as an LED is arranged to face a side surface of thelight guide plate 17 in an opposed manner.

The light guide plate 17 is arranged in a state that one side surface ofthe light guide plate 17 faces the light source 18 in an opposed manner,and the light guide plate 17 is stored in the mold frame 16 on a sideopposite to a side of the mold frame 16 in which the liquid crystaldisplay panel is stored. Further, the reflection sheet 19 arranged belowthe light guide plate 17 is adhered to the mold frame 16 using anadhesive agent applied to a periphery of the reflection sheet 19.

FIG. 2 shows the cross-sectional constitution of the liquid crystaldisplay module of the invention taken along a line A-A′ in FIG. 1. FIG.2 shows a state that the liquid crystal display module shown in FIG. 1is stored in a space defined by an upper frame 21 and a lower frame 22.Further, FIG. 3 shows the cross-sectional constitution of theconventional liquid crystal display module taken along a line B-B′ inFIG. 1. FIG. 3 also shows a state that the liquid crystal display moduleshown in FIG. 1 is stored in the space defined by the upper frame 21 andthe lower frame 22 in the same manner as FIG. 2.

As shown in FIG. 2, in the invention, the other end of the flexibleprinted circuit board 15 (a portion of the flexible printed circuitboard 15 on which the light source 18 is arranged and which is arrangedon a bottom surface of the lower frame 22) is configured to overlap aportion of the reflection sheet 19 and, further, an insulation sheet 20is arranged between the other end of the flexible printed circuit board15 and the reflection sheet 19.

FIG. 3 is the cross-sectional view taken along the line B-B′ in FIG. 1of the liquid crystal display module. As shown in FIG. 3, the other endof the flexible printed circuit board 15 is not brought into contactwith the reflection sheet 19 directly but is brought into contact withthe insulation sheet 20. By arranging such an insulation sheet 20, apushing force applied to the reflection sheet 19 from the flexibleprinted circuit board 15 is alleviated or reduced and hence, it ispossible to provide a liquid crystal display module having no displayirregularities.

The insulation sheet 20 of the invention is explained in detail inconjunction with FIG. 4.

FIG. 4 is a view showing the technique feature of the invention. FIG. 4shows a state that the other end of the flexible printed circuit board15 and the insulation sheet 20 arranged on the other end of the flexibleprinted circuit board 15.

The insulation sheet 20 may be formed of a member having a smoothsurface such as a polyethylene terephthalate (PET) sheet, for example.To acquire an advantageous effect of the invention, that is, to satisfya demand for the reduction of thickness of a liquid crystal displaymodule in general, it is confirmed necessary to set a thickness t1 ofthe insulation sheet 20 to a value not less than 35 μm and not more than45 μm to provide a liquid crystal display module having no displayirregularities while satisfying the demand for the reduction ofthickness. Here, by setting the thickness t1 to a value not less than 30μm, it is possible to expect the advantageous effects of the inventionto a considerable extent. Further, even when the thickness t1 is set toa value not less than 20 μm, it is possible to expect theabove-mentioned advantageous effect that the display irregularities canbe reduced to some extent. However, when the thickness t1 is set to avalue less than 20 μm, that is, the thickness t1 becomes excessivelysmall, the insulation sheet 20 no more plays a role of alleviating theforce applied from the flexible printed circuit board 15 and hence, itis necessary to set the thickness t1 to 20 μm at minimum. Here, thelarger the thickness t1 of the insulation sheet 20, the force appliedfrom the flexible printed circuit board 15 can be alleviated more.However, the increase of the thickness t1 of the insulation sheet 20 iscontrary to a demand for the reduction of thickness of the liquidcrystal display module in general and hence, it is desirable to set thethickness t1 to the value not more than 40 μm. The thickness t1 of theinsulation sheet 20 may be set to a value equal to or less than 60 μm atmaximum.

Next, the insulation sheet 20 is arranged for alleviating the forceapplied to the reflection sheet 19 from the flexible printed circuitboard 15 and hence, it is considered necessary to overlap the insulationsheet 20 to the other end of the flexible printed circuit board 15(overlapping portion indicated by symbol L1 in FIG. 4) where the forceis most remarkably applied. In the invention, although the insulationsheet 20 may be fixed by an adhesive agent or the like, to take a demandfor the simple constitution and the role of the insulation sheet 20 toalleviate the force applied from the flexible printed circuit bard 15into consideration, it is more preferable to freely insert theinsulation sheet 20 between the flexible printed circuit board 15 andthe reflective sheet 19 instead of fixing the insulation sheet 20 usingan adhesive agent or the like. Accordingly, it is preferable that theinsulation sheet 20 extends to the reflection sheet 19 in a state thatthe insulation sheet 20 gets over the other end of the flexible printedcircuit board 15. That is, the insulation sheet 20 is preferablyarranged on the reflection sheet 19 in a state that the insulation sheet20 gets over the flexible printed circuit board 15 by at least not lessthan 10 mm (L4≧10 mm). Here, provided that a length L2 of the insulationsheet 20 satisfies the relationship of L2≧L4/2 with respect to a storinglength L4 of the insulation sheet 20 in the mold frame 16, there is nopossibility that the insulation sheet 20 is removed even when theinsulation sheet 20 is freely held.

1. A liquid crystal display module comprising: a liquid crystal displaypanel; a backlight device arranged on a back surface of the liquidcrystal display panel, the backlight device being constituted of a lightguide plate and a reflection sheet arranged on a back surface of thelight guide plate; an insulation sheet arranged on a back surface of thelight guide plate; a flexible printed circuit board having one endthereof mounted on the liquid crystal display panel and another endthereof formed on a back surface of the insulating sheet; at least oneLED formed on the flexible print board and faced to the light guideplate; wherein the reflection sheet, the insulation sheet, and theflexible print board extend over different distances from the at leastone LED in this order.
 2. A liquid crystal display module according toclaim 1, wherein a thickness of the insulation sheet is set to a valuenot less than 20 μm and not more than 50 μm.
 3. A liquid crystal displaymodule according to claim 2, wherein a thickness of the insulation sheetis set to a value not less than 30 μm and not more than 50 μm.
 4. Aliquid crystal display module according to claim 3, wherein a thicknessof the insulation sheet is set to a value not less than 35 μm and notmore than 45 μm.
 5. A liquid crystal display module according to claim1, wherein the distance of extension of the insulation sheet from the atleast one LED is greater than the distance of extension of the flexibleprinted circuit board from the at least one LED by at least 10 mm.
 6. Aliquid crystal display module according to claim 2, wherein the distanceof extension of the insulation sheet from the at least one LED isgreater than the distance of extension of the flexible printed circuitboard from the at least one LED by at least 10 mm.
 7. A liquid crystaldisplay module according to claim 1, wherein the insulation sheet ismade of polyethylene terephthalate.
 8. A liquid crystal display moduleaccording to claim 1, wherein thickness of the light guide plate isthicker at an area at a side of the at least one LED than other areas ofthe light guide plate.
 9. A liquid crystal display module according toclaim 8, wherein an optical sheet is arranged between the light guideplate and the liquid crystal display panel.
 10. A liquid crystal displaymodule according to claim 1, wherein the distance of extension of thereflection sheet from the at least one LED is greater than the distanceof extension of the insulation sheet and the flexible printed circuitboard from the at least one LED, and the distance of extension of theflexible printed circuit board from the at least one LED is smaller thanthe distance of extension of the insulation sheet and the reflectionsheet from the at least one LED.